The U.K. needs and extra 1,500 armed officers to tackle terror attacks, but police forces are struggling to find new recruits because candidates fear they will spend years under investigation if they use their weapons, the British top firearms officer told the Guardian.

“We might have a challenge attracting the right number of volunteers and retaining the people we have got,” Deputy Chief Constable Simon Chesterman said. “It is not a crisis but it might become one.”

Britain’s officers volunteer to carry a gun. There are currently 5,647 firearms-carrying officers in the U.K. and security officials are looking for 3,000 volunteers to compete for 1,500 new available spots, calculating that half won’t make it through the training and selection process.

Increasing the number of firearms officers is part of a plan following the November Paris terror attacks.

Officials warn that significant parts of the country are vulnerable to a Paris or Brussels-style attack due to a lack of armed officers.

“Currently there are not enough firearms officers who could deal with an incident in quite a lot of areas of Britain,” said Che Donald of the Police Federation.

Chesterman said: “Morale among firearms officers is poor … What they are worried about, in the event they have to use lethal force, is that they make a split-second decision and are pulled apart for up to 10 years.”